Polyaminoamide based resins have been used for over forty years in the manufacture of paper under neutral and alkaline conditions. Furthermore, in the paper industry, polyaminoamides made from dibasic acids and polyamines are commonly used as pre-polymers for the synthesis of polyaminoamide-epichlorohydrin (PAE) resins (e.g. H. H. Espy, TAPPI J., 78, 90 (1995)). Typically, to result in a resin, a polyaminoamide is treated with epichlorohydrin, which reacts with the secondary amines in the polymer backbone to form chlorohydrin, azetidinium or epoxide functionalities necessary for self-crosslinking and reacting with the cellulosic pulp fiber as shown in U.S. Pat. Nos. 2,926,116; 2,926,154; 3,332,901; 5,644,021; 6,222,006; and 5,668,246.
The procedures for making polyaminoamide-epihalohydrin resins are well known in the art. However, with respect to making the polyaminoamides, typical processes produce polyaminoamides having a high molecular weight and a wide molecular weight distribution and are generally prepared using a 1:1 mole ratio of dibasic acid and polyamine. The high molecular weight of the polyaminoamide, when later converted to a resin, limits the level of solids at which the resin can be prepared and stored while still maintaining a high level of performance. As a result, the concentration of resin solids are in the range of about 10 wt.-% to about 30 wt.-% of the resin, but are generally limited to a maximum of about 30 wt.-%. At present, there is a need within the industry to provide high solids resins having the capacity to undergo long periods of storage while maintaining a level of performance substantially equal to those resins having a lowers solids content.
Recently, the approach to synthesizing high solids resins has involved reducing the molecular weight of the polyaminoamide via an endcapping technique using a monobasic acid to control the growth of the polymer chains and the molecular weight distribution. Conversion of such polyaminoamides to resins through reaction with epihalohydrins has produced resin solids as high as 40%. However these types of processes necessitate the handling of extra ingredients not required by the present invention. Thus, the present invention provides for a simpler, more efficient process than those currently used in the art.
There are several distinct advantages conferred by the present invention. First, the present invention allows one to control the molecular weight of the polyaminoamide via the increased polyamine:dibasic acid/ester mole ratio producing a low molecular weight polymer with a narrow molecular weight distribution. Second, the additional amine groups resulting from the increased polyamine:dibasic acid/ester mole ratio provide additional sites for reaction with epihalohydrin, thus giving potentially higher reactive functionality. Third, the combination of low molecular weight and a narrow molecular weight distribution allows for the synthesis of high solids resins having good storage stability and performance.